Greene had not played in a NFL game in two years but was granted another chance by the Chiefs in January, when he signed a futures contract. He previously worked out for the team during the 2016 season but did not sign then.
A futures contract is the same as a regular active-roster contract with veteran minimum salaries, cap regulations and bonuses. Teams can sign free agents to a futures contract as soon as the regular season ends, but the contract doesn't take effect until the start of the next business year, which, in the NFL, happened March 9.